The disclosure of Japanese Patent Application No. 2000-317737 filed on Oct. 18, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an internal combustion engine fuel injection apparatus and a control method thereof.
2. Description of Related Art
Recently, with regard to the fuel injection apparatus of internal combustion engines, there is a demand for high precision in regulating the amount of fuel injected due to the need to perform a fine fuel injection control in accordance with the state of operation of an engine. For example, Japanese Patent Application Laid-Open No. 7-239050 discloses a technology in which a single armature for driving a needle valve is driven by using a valve-opening solenoid coil and a valve-closing solenoid coil that are independent from each other. The result of this technology is that the bouncing oscillation of the needle valve at the open/closing time is reduced and the precision regarding the amount of fuel injected is improved.
As for the timing of starting electrification of the valve-closing solenoid coil in the above-described conventional fuel injection apparatus, the electrification of the valve-closing solenoid coil is started at an overlap time prior to the stop of electrification of the valve-opening solenoid coil, so as to quickly and reliably perform the valve closing action. The xe2x80x9coverlap timexe2x80x9d herein refers to a time between a start of electrification of the valve-closing solenoid coil and the end of electrification of the valve-opening solenoid coil. After electrification of the valve-closing solenoid coil is started, the current through the valve-closing solenoid coil gradually increases. Thus, a certain time is required before the current through the valve-closing solenoid coil reaches a predetermined value that will cause the solenoid coil to produce a predetermined magnetic attraction force. Therefore, it is necessary to set an overlap time. The overlap time may also be termed xe2x80x9cmagnetization delay timexe2x80x9d of the valve-closing solenoid coil.
More specifically, when a voltage is applied to a solenoid coil, current flows through the solenoid coil, so that a magnetic flux produced by the current produces a magnetic attraction force that attracts the armature. The current through the solenoid coil gradually increases with a time delay. Therefore, the magnetic attraction force, which is proportional to the magnitude of current, also gradually increases with a time delay. Hence, in order to produce a magnetic attraction force that immediately moves the needle valve in the valve-closing direction simultaneously with a stop of electrification of the valve-opening solenoid coil, the overlap time is set to an amount of delay time that is needed for the current through the valve-closing solenoid coil to reach a predetermined value. With such setting of the overlap time, the needle valve is moved in the valve-closing direction to close the fuel injection hole simultaneously with the stop of electrification of the valve-opening solenoid coil. Thus, a high-precision control of the fuel injection amount can be achieved.
In this case, the amount of fuel injection is determined by the open valve duration of the fuel injection valve. Therefore, variable factors in the electrification control are the timing of starting electrifying the valve-opening solenoid coil and the duration of its electrification. The aforementioned overlap time, that is, the time between the timing of starting electrifying the valve-closing solenoid coil and the stop of electrification of the valve-opening solenoid coil, is kept constant.
If the amount of fuel injection, the shape of fuel spray, or the like is to be changed in accordance with the state of operation of the internal combustion engine, the fuel pressure supplied to the fuel injection apparatus is changed in some cases, particularly in a direct injection type internal combustion engine or the like. If in such an engine, the fuel pressure supplied to the fuel injection apparatus is raised, the raised fuel pressure increases the force that urges the needle valve disposed within the fuel passage in the valve-closing direction. In correspondence with the amount of increase in the urging force in the valve-closing direction (caused by the increase in fuel pressure), the value of current that produces a magnetic attraction force needed to move the needle valve in the valve-closing direction is reduced. However, if the overlap time is fixed, the aforementioned reduced value of current is reached prior to the timing of stopping electrifying the valve-opening solenoid coil. Consequently, as the magnetic attraction force needed to move the needle valve in the valve-closing direction is reached (i.e., prior to the timing of stopping electrifying the valve-opening solenoid), the needle valve is driven in the valve-closing direction. Therefore, the needle valve is closed at an earlier timing. That is, the raised fuel pressure results in an open valve duration that is shorter than a control-targeted open valve duration. Hence, the problem of a reduced amount of fuel injection may occur.
Accordingly, it is an object of the invention to provide an internal combustion engine fuel injection apparatus having a valve-opening solenoid coil and a valve-closing solenoid coil which is capable of curbing the reduction in the amount of fuel injection caused by a failure in achieving a control-targeted open valve duration if the fuel pressure supplied to the fuel injection apparatus is raised in accordance with the state of operation of an internal combustion engine, and is therefore capable of regulating the amount of fuel injection with even higher precision.
In order to achieve the above and/or other objects, one aspect of the invention provides a fuel injection apparatus of an internal combustion engine including a valve body movably disposed for back and forth movement in a fuel passage to open and close a fuel injection hole of the fuel injection apparatus. An armature is attached to the valve body. A valve-opening solenoid coil drives the armature in a valve-opening direction. A valve-closing solenoid coil drives the armature in a valve-closing direction. A controller that sets an overlap time, which is a time by which starting of electrifying of the valve-closing solenoid coil precedes stopping of electrifying of the valve-opening solenoid coil, controls the solenoid coils in accordance with a fuel pressure supplied to the fuel injection apparatus such that a valve-closing force on the valve body does not exceed an open valve holding force on the valve body prior to the time when stopping of the electrifying of the valve-opening solenoid coil occurs.
Furthermore, in order to achieve the aforementioned and/or other objects, the invention also provides a control method of a fuel injection apparatus of an internal combustion engine, the fuel injection apparatus including a valve body movably disposed for back and forth movement in a fuel passage to open and close a fuel injection hole of the fuel injection apparatus, an armature attached to the valve body, a valve-opening solenoid coil to drive the armature in a valve-opening direction, and a valve-closing solenoid coil to drive the armature in a valve-closing direction. The control method includes the steps of: setting an overlap time, which is a time by which starting of electrifying of the valve-closing solenoid coil precedes stopping of electrifying of the valve-opening solenoid coil; and controlling the solenoid coils in accordance with a fuel pressure supplied to the fuel injection apparatus such that a valve-closing force on the valve body does not exceed an open valve holding force on the valve body prior to the time when stopping of the electrifying of the valve-opening solenoid coil occurs.
According to the internal combustion engine fuel injection apparatus and control method described above, a control is performed in accordance with the fuel pressure supplied to the fuel injection apparatus such that the valve-closing force on the valve body does not exceed the open valve holding force on the valve body prior to the time when stopping of the electrifying of the valve-opening solenoid coil occurs, even if the supplied fuel pressure changes. Therefore, even if the fuel pressure is set high, the open valve holding force on the valve body can be maintained by offsetting the amount of increase in the valve-closing force on the valve body. Hence, it is possible to substantially prevent a reduction in the open valve duration of the valve body and therefore prevent a reduction in the amount of fuel injected. Thus, the amount of fuel injection can be regulated with high precision.